1. Field of the Invention
The subject invention relates to a transmission and torque limiting assembly intended for use in transmitting rotation from a drive to a compressor.
2. Description of the Related Art
Various torque limiting devices exist in the art that are used in compressors to decouple compressor shafts from driven members such as gears or pulleys. Although they may be used with almost any type of compressor, such devices are often used in compressors lacking an electromagnetically activated device or other type of clutch to engage or disengage the compressor shaft from the driven member. Referred to as a “clutchless” compressor, this type of compressor has a shaft coupled to a driven member that is in turn coupled to the accessory belt system of an engine. When the engine crankshaft rotates, the belt system rotates, which also causes the driven member and shaft to rotate.
A torque limiting device typically engages both the driven member and the compressor shaft, and transmits the rotation of the driven member to the shaft. Should an unforeseen malfunction occur within the compressor to cause the rotating shaft to seize or “lock up” and resist rotating in the same direction as the driven member, the torque limiting device will disengage the shaft from the driven member. This permits the disengaged driven member to continue rotating, and keeps the shaft from generating and transmitting a damaging reactive force to the engine.
An example of a torque limiting device is disclosed in U.S. Pat. No. 5,706,922 (“Bondioli”). The Bondioli device utilizes multiple components to accomplish the straightforward act of disengaging a pulley from a shaft. In particular, the pulley of the Bondioli device has recesses that cooperate with wedge-shaped sliders. Each slider engages one of several pairs of pads carried by the device. The pads are urged together by underlying springs. The slider engages the pair at the point at which the pads intersect. The slider also engages one of the recesses in the pulley, and pivots in response to a torque applied by the rotating pulley on the slider. This urges the slider against the intersecting edges of the pads, and causes the pads to separate. The underlying springs compress and move away from one another in response. The slider continues to press against the pads and springs until it has pivoted free from the recess on the pulley. Once all of the sliders disengage the recesses, the compressor shaft disengages the pulley.
The Bondioli device is complicated and does not work unless multiple parts simultaneously cooperate to ensure that the compressor shaft is quickly disengaged from the pulley. Because so many components are used, rotation must be transmitted from the pulley to the compressor shaft through several energy-expending, intermittent steps. Thus, the Bondioli device fails to provide an efficient, cost-effective way to disengage a compressor shaft from a pulley or other driven member.